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Friday, 20 September 2013

Animal Kingdom

Question 1:
What are the difficulties that you would face in classification of animals, if common fundamental features are not taken into account?
Answer:
For the classification of living organisms, common fundamental characteristics are considered.
If we consider specific characteristics, then each organism will be placed in a separate group and the entire objective of classification would not be achieved.
Classification of animals is also important in comparing different organisms and judging their individual evolutionary significance. If only a single characteristic is considered, then this objective would not be achieved.

Question 2:
If you are given a specimen, what are the steps that you would follow to classify it?
Answer:
There is a certain common fundamental feature that helps in classification of living organisms. The features that can be used in classification are as follows.
On the basis of above features, we can easily classify a specimen into its respective category.

Question 3:
How useful is the study of the nature of body cavity and coelom in the classification of animals?
Answer:
Coelom is a fluid filled space between the body wall and digestive tract. The presence or absence of body cavity or coelom plays a very important role in the classification of animals. Animals that possess a fluid filled cavity between body wall and digestive tract are known as coelomates. Annelids, mollusks, arthropods, echinodermates, and chordates are examples of coelomates. On the other hand, the animals in which the body cavity is not lined by mesoderm are known as pseudocoelomates. In such animals, mesoderm is scattered in between ectoderm and endoderm. Aschelminthes is an example of pseudocoelomates. In certain animals, the body cavity is absent. They are known as acoelomates. An example of acoelomates is platyhelminthes.

Question 4:
Distinguish between intracellular and extracellular digestion?
Answer:
Intracellular digestion
Extracellular digestion
1.
The digestion of food occurs within the cell.
1.
The digestion occurs in the cavity of alimentary canal.
2.
Digestive enzymes are secreted by the surrounding cytoplasm into the food vacuole.
2.
Digestive enzymes are secreted by special cells into the cavity of alimentary canal.
3.
Digestive products are diffused into the cytoplasm.
3.
Digestive products diffuse across the intestinal wall into various parts of the body.
4.
It is a less efficient method.
4.
It is a more efficient method of digestion.
5.
It occurs in unicellular organisms.
5.
It occurs in multicellular organisms.
 

Question 5:
What is the difference between direct and indirect development?
Answer:
Direct development
Indirect development
1.
It is a type of development in which an embryo develops into a mature individual without involving a larval stage.
1.
It is a type of development that involves a sexually-immature larval stage, having different food requirements than adults.
2.
Metamorphosis is absent.
2.
Metamorphosis involving development of larva to a sexually-mature adult is present.
3.
It occurs in fishes, reptiles, birds, and mammals.
3.
It occurs in most of the invertebrates and amphibians.
 

Question 6:
What are the peculiar features that you find in parasitic platyhelminthes?
Answer:
Taenia (Tapeworm) and Fasciola (liver fluke) are examples of parasitic platyhelminthes.
Peculiar features in parasitic platyhelminthes are as follows.
1. They have dorsiventrally flattened body and bear hooks and suckers to get attached inside the body of the host.
2. Their body is covered with thick tegument, which protects them from the action of digestive juices of the host.
3. The tegument also helps in absorbing nutrients from the host’s body.

Question 7:
What are the reasons that you can think of for the arthropods to constitute the largest group of the animal kingdom?
Answer:
The phylum, Arthropoda, consists of more than two-thirds of the animal species on earth. The reasons for the success of arthropods are as follows.
  1. Jointed legs that allow more mobility on land
  2. Hard exoskeleton made of chitin that protects the body
  3. The hard exoskeleton also reduces water loss from the body of arthropods making them more adapted to terrestrial conditions.

    Question 8:
    Water vascular system is the characteristic of which group of the following:
    (a) Porifera (b) Ctenophora (c) Echinodermata (d) Chordata
    Answer:
    Water vascular system is a characteristic feature of the phylum, Echinodermata. It consists of an array of radiating channels, tube feet, and madreporite. The water vascular system helps in locomotion, food capturing, and respiration.

    Question 9:
    “All vertebrates are chordates but all chordates are not vertebrates”. Justify the statement.
    Answer:
    The characteristic features of the phylum, Chordata, include the presence of a notochord and paired pharyngeal gill slits. In sub-phylum Vertebrata, the notochord present in embryos gets replaced by a cartilaginous or bony vertebral column in adults. Thus, it can be said that all vertebrates are chordates but all chordates are not vertebrates.

    Question 10:
    How important is the presence of air bladder in Pisces?
    Answer:
    Gas bladder or air bladder is a gas filled sac present in fishes. It helps in maintaining buoyancy. Thus, it helps fishes to ascend or descend and stay in the water current.

    Question 11:
    What are the modifications that are observed in birds that help them fly?
    Answer:
    Birds have undergone many structural adaptations to suit their aerial life. Some of these adaptations are as follows.
    (i) Streamlined body for rapid and smooth movement
    (ii) Covering of feathers for insulation
    (iii) Forelimbs modified into wings and hind limbs used for walking, perching, and swimming
    (iv) Presence of pneumatic bones to reduce weight
    (v) Presence of additional air sacs to supplement respiration

    Question 12:
    Could the number of eggs or young ones produced by an oviparous and viviparous mother be equal? Why?
    Answer:
    The numbers of eggs produced by an oviparous mother will be more than the young ones produced by a viviparous mother. This is because in oviparous animals, the development of young ones takes place outside the mother’s body. Their eggs are more prone to environmental conditions and predators. Therefore, to overcome the loss, more eggs are produced by mothers so that even under harsh environmental conditions, some eggs might be able to survive and produce young ones. On the other hand, in viviparous organisms, the development of young ones takes place in safe conditions inside the body of the mother. They are less exposed to environmental conditions and predators. Therefore, there are more chances of their survival and hence, less number of young ones is produced compared to the number of eggs.

    Question 13:
    Segmentation in the body is first observed in which of the following:
    (a) Platyhelminthes (b) Aschelminthes (c) Annelida (d) Arthropoda
    Answer:
    The body segmentation first appeared in the phylum, Annelida (annulus meaning little ring).

    Question 14:
    Match the following: 
    (a) Operculum(i) Ctenophora
    (b) Parapodia(ii) Mollusca
    (c) Scales(iii) Porifera
    (d) Comb plates(iv) Reptilia
    (e) Radula(v) Annelida
    (f) Hairs(vi) Cyclostomata and Chondrichthyes
    (g) Choanocytes(vii) Mammalia
    (h) Gill slits(viii) Osteichthyes

    Answer:
     
    Column I
    		 
    Column II
    (a)
    Operculum
    (viii)
    Osteichthyes
    (b)
    Parapodia
    (v)
    Annelida
    (c)
    Scales
    (iv)
    Reptilia
    (d)
    Comb plates
    (i)
    Ctenophora
    (e)
    Radula
    (ii)
    Mollusca
    (f)
    Hairs
    (vii)
    Mammalia
    (g)
    Choanocytes
    (iii)
    Porifera
    (h)
    Gill slits
    (vi)
    Cyclostomata and Chondrichthyes
    Question 15:
    Prepare a list of some animals that are found parasitic on human beings.
    Answer:
    S. No.
    Name of organism
    Phylum
    1
    Taenia solium
    Platyhelminthes
    2
    Fasciola hepatica
    Platyhelminthes
    3
    Ascaris lumbricoides
    Aschelminthes
    4
    Wuchereria bancrofti
    Aschelminthes
    5
    Ancyclostoma
    Aschelminthes
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Plant Kingdom

Question 1:
What is the basis of classification of algae?
Answer:
Algae are classified into three main classes – Chlorophyceae, Phaeophyceae, and Rhodophyceae. These divisions are based on the following factors:
(a) Major photosynthetic pigments present
(b) Form of stored food
(c) Cell wall composition
(d) Number of flagella and position of insertion
Class I – Chlorophyceae
Common name – Green algae
Major pigments – Chlorophylls a and b
Stored food – Starch
Cell wall composition – Cellulose
Flagella number and position – 28; equal and apical
Class II – Phaeophyceae
Common name– Brown algae
Major pigments – Chlorophylls a and c, and fucoxanthin
Stored food – Mannitol and laminarin
Cell wall composition – Cellulose and algin
Flagella number and position – 2; unequal and lateral
Class III­ – Rhodophyceae
Common name – Red algae
Major pigments – Chlorophylls a and b, and phycoerythrin
Stored food –­ Floridean starch
Cell wall – Cellulose, pectin, and polysulphate esters
Flagella number – Absent

Question 2:
When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?
Answer:
Liverwort – In liverworts, the main plant-body is haploid (gametophytic). It bears the male and female sex organs which produce gametes. These gametes fuse to form a zygote. The zygote develops on the gametophytic plant-body to form a sporophyte. The sporophyte is differentiated into the foot, seta, and capsule. Many haploid spores are produced as a result of the reduction division taking place inside the capsule.
Moss – In mosses, the primary protonema (developed in the first stage) develops into the secondary protonema. Both these stages are haploid or gametophytic. The secondary protonema bears the sex organs which produce gametes. These gametes fuse to form a zygote. The zygote develops into a sporophyte. Many spores are formed as a result of the reduction division taking place in the capsule of this sporophyte.
Fern – In ferns, the main plant-body is sporophytic. Its leaves are known as sporophylls and these bear the sporangia. Reduction division takes place in these sporangia, thereby producing many spores.
Gymnosperm – In gymnosperms, the main plant-body is sporophytic. They bear two types of leaves – microsporophylls and megasporophylls. Reduction division takes place in the microsporangia present on the microsporophylls (producing pollen grains) and on the megasporangia present on the megasporophylls (producing megaspores).
Angiosperm – In angiosperms, the main plant-body is sporophytic and bears flowers. The male sex organ in the flower is the stamen, while the female sex organ is the pistil. Reduction division takes place in the anthers of the stamen (producing haploid pollen grains) and in the ovary of the pistil (producing eggs)

Question 3:
Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Answer:
Archegonium is the female sex organ that produces the female gamete or egg. It is present in the life cycles of bryophytes, pteridophytes, and gymnosperms.
Life cycle of a fern (Dryopteris)
Dryopteris is a common fern with pinnately-compound leaves. The main plant-body is sporophytic. Many sporangia are borne on the lower surfaces of its mature leaves. Each sporangium has spore mother cells which undergo meiosis to produce haploid spores. On maturing, these spores dehisce and germinate to give rise to a heart-shaped gametophyte called prothallus.
The prothallus bears the male and female sex organs called antheridia and archegonia respectively. The antheridia produce sperms that swim in water to reach the archegonia. The egg is produced by the archegonia. As a result of fertilisation, a zygote is formed. The zygote forms an embryo, which in turn develops into a new sporophyte. The young plant comes out of the archegonium of the parent gametophyte.

Question 4:
Mention the ploidy of the following: protonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a fern; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.
Answer:
(a) Protonemal cell of a moss – Haploid
(b) Primary endosperm nucleus in a dicot – Triploid
(c) Leaf cell of a moss – Haploid
(d) Prothallus of a fern – Haploid
(e) Gemma cell in Marchantia – Haploid
(f) Meristem cell of a monocot – Diploid
(g) Ovum of a liverwort – Haploid
(h) Zygote of a fern – Diploid

Question 5:
Write a note on economic importance of algae and gymnosperms.
Answer:
Economic importance of algae
Algae have diverse economic uses. They perform half of the total carbon dioxide-fixation on earth by photosynthesis, acting as the primary producers in aquatic habitats.
(a) Food source: Many species of marine algae such as Porphyra, Sargassum, and Laminaria are edible. Chlorella and Spirulina are rich in proteins. Thus, they are used as food supplements.
(b) Commercial importance: Agar is used in the preparation of jellies and ice-cream. It is obtained from Gelidium and Gracilaria. Carrageenin is used as an emulsifier in chocolates, paints, and toothpastes. It is obtained from the red algae.
(c) Medicines: Many red algae such as Corallina are used in treating worm infections.
Economic importance of gymnosperms
(a) Construction purposes: Many conifers such as pine, cedar, etc., are sources of the soft wood used in construction and packing.
(b) Medicinal uses: An anticancer drug Taxol is obtained from Taxus. Many species of Ephedraproduce ephedrine, which can be used in the treatment of asthma and bronchitis.
(c) Food source: The seeds of Pinus gerardiana (known as chilgoza) are edible.
(d) Source of resins: Resins are used commercially for manufacturing sealing waxes and water-proof paints. A type of resin known as turpentine is obtained from various species of Pinus.

Question 6:
Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
Answer:
Gymnosperms and angiosperms are seed-producing plants with diplontic life cycles.
In gymnosperms, the sporophylls are aggregated to form compact cones. The microsporophylls are broad and are not distinguished into filaments and anthers. The megasporophylls are woody and lack the ovary, style, and stigma, because of which the ovules lie exposed. The female gametophyte consists of archegonia. The fertilisation process involves the fusion of a male gamete with the female gamete. Their endosperm is haploid. The produced seeds are naked as there is no fruit formation.
Angiosperms are also known as flowering plants. They have sporophylls that aggregate to form flowers with the perianth. The microsporophylls consist of stamens containing pollen sacs. These sacs bear the male gametes called pollen grains. The megasporophylls are delicate and rolled, forming carpels that contain the ovary, style, and stigma. The ovules are present inside the ovary. The archegonium is replaced by an egg apparatus. Two male gametes enter the egg apparatus at the time of fertilisation. One male gamete fertilises the egg and the other fuses with the diploid secondary nucleus to form an endosperm. The resulting endosperm is thus triploid. In addition, in angiosperms, the development of seeds takes place inside the fruits.

Question 7:
What is heterospory? Briefly comment on its significance. Give two examples.
Answer:
Heterospory is a phenomenon in which two kinds of spores are borne by the same plant. These spores differ in size. The smaller one is known as microspore and the larger one is known as megaspore. The microspore germinates to form the male gametophyte and the megaspore germinates to form the female gametophyte. The male gametophyte releases the male gametes and these reach the female gametophyte to fuse with the egg. The development of the zygote takes place inside the female gametophyte.
This retention and germination of the megaspore within the megasporangium ensures proper development of the zygote. The zygote develops into the future sporophyte. The evolution of the seed habit is related to the retention of the megaspore.
Heterospory is thus considered an important step in evolution as it is a precursor to the seed habit.
Heterospory evolved first in pteridophytes such as Selaginella and Salvinia.

Question 8:
Explain briefly the following terms with suitable examples:-
(i) protonema
(ii) antheridium
(iii) archegonium
(iv) diplontic
(v) sporophyll
(vi) isogamy
Answer:
(i) Protonema – It is the first stage in the life cycle of a moss, developing directly from the spore. It consists of creeping, green, branched, and often filamentous structures.
(ii) Antheridium – It is the male sex organ present in bryophytes and pteridophytes and is surrounded by a jacket of sterile cells. It encloses the sperm mother cells, which give rise to the male gametes.
(iii) Archegonium – It is the female sex organ present in bryophytes, pteridophytes, and gymnosperms. In bryophytes and pteridophytes, it generally has a swollen venter and a tubular neck, and contains the female gamete called the egg.
(iv) Diplontic – It is the term used for the life cycles of seed-bearing plants (gymnosperms and angiosperms). In these plants, the diploid sporophyte is dominant, photosynthetic, and independent. The gametophyte is represented by a single-celled (or a few-celled) structure.
(v) Sporophyll – In pteridophytes, the sporophytic plant body bears sporangia. These sporangia are subtended by leaf-like appendages known as sporophylls. In gymnosperms, microsporophylls and megasporophylls are found. These bear microspores and megaspores respectively.
(vi) Isogamy – It is a type of sexual reproduction involving the fusion of morphologically-similar gametes. This means that the gametes are of the same size, but perform different functions. This type of reproduction is commonly observed in Spirogyra.

Question 9:
Differentiate between the following:-
(i)red algae and brown algae
(ii) liverworts and moss
(iii) homosporous and heterosporous pteridophyte
(iv) syngamy and triple fusion
Answer:
(i) Red algae and brown algae
Red algae
Brown algae
1.
Red algae are grouped under the class Rhodophyceae.
1.
Brown algae are grouped under the class Phaeophyceae.
2.
They contain floridean starch as stored food.
2.
They contain mannitol or laminarin as stored food.
3.
They contain the photosynthetic pigments chlorophylls a and d, and phycoerythrin.
3.
They contain the photosynthetic pigments chlorophylls a and c, and fucoxanthin.
4.
Their cell walls are composed of cellulose, pectin, and phycocolloids.
4.
Their cell walls are composed of cellulose and algin.
5.
Flagella are absent
5.
Two flagella are present
(ii) Liverworts and moss
Liverworts
Moss
1.
They have unicellular rhizoids.
1.
They have multicellular rhizoids.
2.
Scales are present very often
2.
Scales are absent
3.
They are generally thalloid, with dichotomous branching.
3.
They are foliage, with lateral branching.
4.
Gemma cups are present
4.
Gemma cups are absent
5.
Sporophyte has very little photosynthetic tissue
5.
Sporophyte has abundant photosynthetic tissue
(iii) Homosporous and heterosporous pteridophyte
Homosporous pteridophytes
Heterosporous pteridophytes
1.
They bear spores that are of the same type.
1.
They bear two kinds of spores – microspores and megaspores.
2.
They produce bisexual gametophytes.
2.
They produce unisexual gametophytes.
(iv) Syngamy and triple fusion
Syngamy
Triple fusion
1.
It is the process of fusion of the male gamete with the egg in an angiosperm.
1.
It is the process of fusion of the male gamete with the diploid secondary nucleus in an angiosperm.
2.
A diploid zygote is formed as a result of syngamy.
2.
A triploid primary endosperm is formed as a result of triple fusion.
Question 10:
How would you distinguish monocots from dicots?
Answer:
Monocots and dicots can be differentiated through their morphological and anatomical characteristics.
Characteristic
Monocot
Dicot
Morphology
Roots
Fibrous roots
Tap roots
Venation
Generally parallel venation
Generally reticulate venation
Flowers
Trimerous flowers
Pentamerous flowers
Cotyledons in seeds
One
Two
Anatomy
No. of vascular bundles in stem
Numerous
Generally 2 – 6
Cambium
Absent
Present
Leaves
Isobilateral
Dorsiventral
 
Question 11:
Match the followings (column I with column II)
Column I
Column II
(a)
Chlamydomonas
(i)
Moss
(b)
Cycas
(ii)
Pteridophyte
(c)
Selaginella
(iii)
Algae
(d)
Sphagnum
(iv)
Gymnosperm
Answer:
Column I
Column II
(a)
Chlamydomonas
(iii)
Algae
(b)
Cycas
(iv)
Gymnosperm
(c)
Selaginella
(ii)
Pteridophyte
(d)
Sphagnum
(i)
Moss

Question 12:
Describe the important characteristics of gymnosperms.
Answer:
Important features of gymnosperms:
1. The term gymnosperm refers to plants with naked seeds (gymnos – naked, sperma – seeds), i.e., the seeds of these plants are not enclosed in fruits.
2. The plant-body ranges from medium to tall trees and shrubs. The giant redwood tree Sequoia is one of the tallest trees in the world.
3. The root system consists of tap roots. The coralloid roots present in Cycas are associated with nitrogen-fixing cyanobacteria.
4. The stem can be branched (as in Pinus and Cedrus) or un-branched (as in Cycas).
5. The leaves can be simple (as in Pinus)or compound (pinnate in Cycas). The leaves are needle-like, with a thick cuticle and sunken stomata. These help in preventing water loss.
6. Gymnosperms are heterosporous. They bear two kinds of spores – microspores and megaspores.
7. Flowers are absent. The microsporophylls and megasporophylls are arranged to form compact male and female cones.
8. Pollination occurs mostly through wind and pollen grains reach the pollen chamber of the ovule through the micropyle.
9. The male and female gametophytes are dependent on the sporophyte.
10. The seeds contain haploid endosperms and remain uncovered.
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Biological Classification

Question 1:
Discuss how classification systems have undergone several changes over a period of time?
Answer:
The classification systems have undergone several changes with time. The first attempt of classification was made by Aristotle. He classified plants as herbs, shrubs, and trees. Animals, on the other hand, were classified on the basis of presence or absence of red blood cells. This system of classification failed to classify all the known organisms.
Therefore, Linnaeus gave a two kingdom system of classification. It consists of kingdom Plantae and kingdom Animalia. However, this system did not differentiate between unicellular and multicellular organisms and between eukaryotes and prokaryotes. Therefore, there were large numbers of organisms that could not be classified under the two kingdoms.
To solve these problems, a five kingdom system of classification was proposed by R.H Whittaker in 1969. On the basis of characteristics, such as cell structure, mode of nutrition, presence of cell wall, etc., five kingdoms, Monera, Protista, Fungi, Plantae, and Animalia were formed.

Question 2:
State two economically important uses of:
(a) Heterotrophic bacteria
(b) Archaebacteria
Answer:
(a) Heterotrophic bacteria
(1) They act as decomposers and help in the formation of humus.
(2) They help in the production of curd from milk.
(3) Many antibiotics are obtained from some species of bacteria.
(4) Many soil bacteria help in fixation of atmospheric nitrogen.
(b) Archaebacteria
(1) Methane gas is produced from the dung of ruminants by the methanogens.
(2) Methanogens are also involved in the formation of biogas and sewage treatment.

Question 3:
What is the nature of cell-walls in diatoms?
Answer:
The cell walls of diatoms are made of silica. Their cell wall construction is known as frustule. It consists of two thin overlapping shells that fit into each other such as a soap box. When the diatoms die, the silica in their cell walls gets deposited in the form of diatomaceous earth. This diatomaceous earth is very soft and quite inert. It is used in filtration of oils, sugars, and for other industrial purposes.

Question 4:
Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.
Answer:
Algal bloom
Algal bloom refers to an increase in the population of algae or blue-green algae in water, resulting in discoloration of the water body. This causes an increase in the biological oxygen demand (BOD), resulting in the death of fishes and other aquatic animals.
Red-tides
Red tides are caused by red dinoflagellates (Gonyaulax) that multiply rapidly. Due to their large numbers, the sea appears red in colour. They release large amounts of toxins in water that can cause death of a large number of fishes.

Question 5:
How are viroids different from viruses?
Answer:
Viroids were discovered in 1917 by T.O. Denier. They cause potato spindle tuber disease. They are smaller in size than viruses. They also lack the protein coat and contain free RNA of low molecular weight.

Question 6:
Describe briefly the four major groups of Protozoa.
Answer:
Protozoa are microscopic unicellular protists with heterotrophic mode of nutrition. They may be holozoic, saprobic, or parasitic. These are divided into four major groups.
(1) Amoeboid protozoa or sarcodines
They are unicellular, jelly-like protozoa found in fresh or sea water and in moist soil. Their body lacks a periplast. Therefore, they may be naked or covered by a calcareous shell. They usually lack flagella and have temporary protoplasmic outgrowths called pseudopodia. These pseudopodia or false feet help in movement and capturing prey. They include free living forms such as Amoeba or parasitic forms such as Entamoeba.
(2) Flagellated protozoa or zooflagellates
They are free living, non-photosynthetic flagellates without a cell wall. They possess flagella for locomotion and capturing prey. They include parasitic forms such as Trypanosoma, which causes sleeping sickness in human beings.
(3) Ciliated protozoa or ciliates
They are aquatic individuals that form a large group of protozoa. Their characteristic features are the presence of numerous cilia on the entire body surface and the presence of two types of nuclei. All the cilia beat in the same direction to move the water laden food inside a cavity called gullet. They include organisms such as Paramoecium, Vorticella,etc.
(4) Sporozoans
They include disease causing endoparasites and other pathogens. They are uninucleate and their body is covered by a pellicle. They do not possess cilia or flagella. They include the malaria causing parasite Plasmodium.

Question 7:
Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Answer:
Plants have autotrophic mode of nutrition as they contain chlorophyll pigment. Thus, they have the ability to prepare their own food by the process of photosynthesis. However, some insectivorous plants are partially heterotrophic. They have various means of capturing insects so as to supplement their diet with required nutrients derived from insects, causing proliferation of growth. The examples include pitcher plant (Nepenthes), Venus fly trap, bladderwort, and sundew plant.

Question 8:
What do the terms phycobiont and mycobiont signify?
Answer:
Phycobiont refers to the algal component of the lichens and mycobiont refers to the fungal component. Algae contain chlorophyll and prepare food for fungi whereas the fungus provides shelter to algae and absorbs water and nutrients from the soil. This type of relationship is referred to as symbiotic.

Question 9:
Give a comparative account of the classes of Kingdom Fungi under the following:
(i) Mode of nutrition
(ii) Mode of reproduction
Answer:
(A) Phycomycetes- This group of fungi includes members such as Rhizopus, Albugo, etc.
(i) Mode of nutrition
They are obligate parasites on plants or are found on decaying matter such as wood.
(ii) Mode of reproduction
Asexual reproduction takes place through motile zoospores or non-motile aplanospores that are produced endogenously in sporangium.
Sexual reproduction may be of isogamous, anisogamous, or oogamous type. It results in the formation of thick-walled zygospore.
(B) Ascomycetes- This group of fungi includes members such as Penicillium, Aspergillus,Claviceps, and Neurospora.
(i) Mode of nutrition
They are sporophytic, decomposers, parasitic or coprophilous (growing on dung).
(ii) Mode of reproduction
Asexual reproduction occurs through asexual spores produced exogenously, such as conidia produced on conidiophores.
Sexual reproduction takes place through ascospores produced endogenously in sac-like asci and arranged inside ascocarps.
(C) Basidiomycetes- This group of fungi includes members such as Ustilago, Agaricus andPuccinia.
(i) Mode of nutrition
They grow as decomposers in soil or on logs and tree stumps. They also occur as parasites in plants causing diseases such as rusts and smuts.
(ii) Mode of reproduction
Asexual reproduction takes place commonly through fragmentation. Asexual spores are absent.
Sex organs are absent but sexual reproduction takes place through plasmogamy. It involves fusion of two different strains of hyphae. The resulting dikaryon gives rise to a basidium. Four basidiospores are produced inside a basidium.
(D) Deuteromycetes – This group of fungi includes members such as Alternaria, Trichoderma, and Colletotrichum.
(i) Mode of nutrition
Some members are saprophytes while others are parasites. However, a large number act as decomposers of leaf litter.
(ii) Mode of reproduction
Asexual reproduction is the only way of reproduction in deuteromycetes. It occurs through asexual spores called conidia.
Sexual reproduction is absent in deuteromycetes.

Question 10:
What are the characteristic features of Euglenoids?
Answer:
Some characteristic features of Euglenoids are as follows.
  • Euglenoids (such as Euglena) are unicellular protists commonly found in fresh water.
  • Instead of cell wall, a protein-rich cell membrane known as pellicle is present.
  • They bear two flagella on the anterior end of the body.
  • A small light sensitive eye spot is present.
  • They contain photosynthetic pigments such as chlorophyll and can thus prepare their own food. However, in absence of light, they behave similar to heterotrophs by capturing other small aquatic organisms.
  • They have both plant and animal-like features, which makes them difficult to classify.

    Question 11:
    Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.
    Answer:
    Viruses are sub-microscopic infectious agents that can infect all living organisms. A virus consists of genetic material surrounded by a protein coat. The genetic material may be present in the form of DNA or RNA.
    Most of the viruses, infecting plants, have single stranded RNA as genetic material. On the other hand, the viruses infecting animals have single or double stranded RNA or double stranded DNA.
    Bacteriophages or viruses infecting bacteria mostly have double stranded DNA. Their protein coat called capsid is made up of capsomere subunits. These capsomeres are arranged in helical or polyhedral geometric forms.
    A.I.D.S, small pox, mumps, and influenza are some common examples of viral diseases.

    Question 12:
    Organise a discussion in your class on the topic- Are viruses living or non-living?
    Answer:
    Viruses are microscopic organisms that have characteristics of both living and non-living. A virus consists of a strand of DNA or RNA covered by a protein coat. This presence of nucleic acid (DNA or RNA) suggests that viruses are alive. In addition, they can also respond to their environment (inside the host cell) in a limited manner.
    However, some other characters, such as their inability to reproduce without using the host cell machinery and their acellular nature, indicate that viruses are non-living. Therefore, classifying viruses has remained a mystery for modern systematics.
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The Living World

Question 1:

Why are living organisms classified?
Answer:

A large variety of plants, animals, and microbes are found on earth. All these living organisms differ in size, shape, colour, habitat, and many other characteristics. As there are millions of living organisms on earth, studying each of them is impossible. Therefore, scientists have devised mechanisms to classify all living organisms. These methods of classification are based on rules and principles that allow identification, nomenclature, and finally classification of an organism.
For example, based on certain principles, once an organism is identified as an insect, it will be given a scientific name and then grouped with other similar organisms. Thus, various groups or taxon include organisms based on their similarity and differences.
Therefore, the biological classification helps in revealing the relationship between various organisms. It also helps in making study of organisms easy and organized.

Question 2:

Why are the classification systems changing every now and then?
Answer:

Millions of plants, animals, and microorganisms are found on earth. Many of these have been identified by the scientists while many new species are still being discovered around the world. Therefore, to classify these newly discovered species, new systems of classification have to be devised every now and then. This creates the requirement to change the existing systems of classification.

Question 3:

What different criteria would you choose to classify people that you meet often?
Answer:

To classify a class of forty students, let us start the classification on the basis of sexes of the students. This classification will result in the formation of two major groups- boys and girls.
Each of these two groups can be further classified on the basis of the names of the students falling in these groups.
Since it is possible that more than one student can have a particular name, these names can be further divided based on the surnames.
Since there is still some chance that more than one student can have the same surname, the final level of classification will be based on the roll numbers of each student.

Question 4:

What do we learn from identification of individuals and populations?
Answer:

The knowledge of characteristics of an individual or its entire population helps in the identification of similarities and dissimilarities among the individuals of same kind or between different types of organisms. It helps the scientists to classify organisms in various categories.

Question 5:

Given below is the scientific name of Mango. Identify the correctly written name.
Mangifera Indica
Mangifera indica
Answer:

In binomial system of nomenclature, the generic name of a species always starts with a capital letter whereas the specific name starts with a small letter. Therefore, the correct scientific name of Mango isMangifera indica.

Question 6:

Define a taxon. Give some examples of taxa at different hierarchical levels.
Answer:

Each unit or category of classification is termed as a taxon. It represents a rank. For example, the basic level of classification is species, followed by genus, family, order, class, phylum or division, in ascending order. The highest level of classification is known as kingdom.

Question 7:

Can you identify the correct sequence of taxonomical categories?
(a) Species → Order → Phylum → Kingdom
(b) Genus → Species → Order → Kingdom
(c) Species → Genus → Order → Phylum
Answer:

The correct hierarchical arrangement of taxonomic categories in ascending order is
Species → Genus → Family → Order → Class → Phylum → Kingdom
Therefore, both (a) and (c) represent correct sequences of taxonomic categories.
In sequence (b), species should be followed by genus. Therefore, it does not represent the correct sequence.

Question 8:

Try to collect all the currently accepted meanings for the word ‘species’. Discuss with your teacher the meaning of species in case of higher plants and animals on one hand and bacteria on the other hand.
Answer:

In biological terms, species is the basic taxonomical rank. It can be defined as a group of similar organisms that are capable of interbreeding under natural conditions to produce fertile offsprings.
Therefore, a group of similar individuals that are respectively isolated form a species.
Species can also be defined as group of individuals that share the same gene pool.

Question 9:

Define and understand the following terms:
(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus
Answer:

(i) Phylum
Phylum is the primary division of kingdom. It includes one or more related classes of animals. In plants, instead of phylum, the term ‘division’ is used.
(ii) Class
Class is a taxonomic group consisting of one or more related orders. For example, the class, Mammalia, includes many orders.
(iii) Family
Family is a taxonomic group containing one or more related genera. In plants, families are categorized on the basis of vegetative and reproductive features.
(iv) Order
Order is a taxonomic group containing one or more families. For example, the order, carnivore, includes many families.
(v) Genus
Genus is a taxonomic group including closely related species. For example, the genus, Solanum, includes many species such as nigrum, melongena, tuberosum,etc.

Question 10:

How is a key helpful in the identification and classification of an organism?
Answer:

Key is another taxonomical aid that helps in identification of plant and animal species. These keys are based on similarities and dissimilarities in characters, generally in a pair called couplet.
Each statement in a taxonomic key is referred to as a lead. For categorizing each taxonomic rank, such as family, genus, species, etc., different keys are used. It is also useful in identification of unknown organisms.
Keys are of two types- indented and bracketed keys. Indented key provides a sequence of choices between two or more statements while in bracketed key, a pair of contrasting characters are used.
(i) Indented key to identify different species of Rhododendron.
1. Leaves evergreen
2. leaves densely hairy below, orange or white hair; flower
appears to have separate petals
………………………. Rhododendron groenlandicum
2. hair absent on leaves, flower has five petals fused in a shallow
tube
………………………. Rhododendron maximus
1. Leaves deciduous
3. pink flowers with two free petals and three fused petals
………………………. Rhododendron canadense
3. white to pink flowers with all petals fused together
(ii) Bracketed key to identify different species of Rhododendron.
  1. Leaves evergreen-----------------------------------------------2
1. Leaves deciduous-----------------------------------------------3
2. Leaves densely hairy below, orange or white hair; flower
appears to have separate petals
……….………………………. Rhododendron groenlandicum
2. Hair absent on leaves, flower has five petals fused in shallow
tube
………………………………..Rhododendron maximus
3. Pink flowers with two free petals and three fused petals
……………………………… Rhododendron canadense
3. White to pink flowers with all petals fused together-----4

Question 11:

Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Answer:

The arrangement of various taxa in a hierarchical order is called taxonomic hierarchy.
In this hierarchy, species is present at the lowest level whereas kingdom is present at the highest level.
Kingdom
↑
Phylum or division
↑
Class
↑
Order
↑
Family
↑
Genus
↑
Species
A Taxonomic hierarchy
Classification of a plant
As an example, let us classify Solanum melongena (Brinjal).
Kingdom – Plantae
Division – Angiospermae
Class – Dicotyledonae
Order – Solanales
Family – Solanaceae
Genus – Solanum
Species – melongena
Classification of an animal
As an example, let us classify Columba livia (Blue rock Dove).
Kingdom – Animalia
Phylum – Chordata
Class – Aves
Order – Columbiformes
Family – Columbidae
Genus – Columba
Species – livia


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